Recent DOE Sponsored Electrochemical Capacitor Test Results
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INTRODUCTION In 1991, the U.S. Department of Energy (DOE) established a program to develop and evaluate electrochemical capacitors (ultracapacitors) as an enabling electric/hybrid vehicle technology [1]. A number of highly promising materials have been studied for use as electrochemical capacitor electrodes that use both Faradaic and non-Faradaic processes for charge separation and storage. These include carbon, conducting doped and undoped pol-ymers, and metal oxides in conjunction with aqueous and non-aqueous electrolytes. The technical targets established by the Partnership for a New Generation of Vehicles (PNGV) for the fastresponse engine specified a specific energy of 6 to 18 Whr/kg, a specific power of 600 to 1800 W/kg, and a volumetric energy density of 9 to 24 Whr/liter. A cycle life of greater than 400k, and a production cost of $320/kWhr were also proposed. Coordination of the development, testing and evaluation of prototype capacitors is the responsibility of the Idaho National Engineering and Environmental Laboratory (INEEL). This paper describes the room temperature (23 'C) constant-current and constant-power test results obtained on prototype capacitors prepared by SAFT America, Inc., and Maxwell Energy Products, Inc. These devices were tested according to test procedures developed at the INEEL [2].
381 Mat. Res. Soc. Symp. Proc. Vol. 575 0 2000 Materials Research Society
DISCUSSION OF TEST RESULTS Ten capacitors were received from SAFT America, Inc. for testing by the Idaho National Engineering and Environmental Laboratory (INEEL) Automotive Systems and Technology (AS&T) Department's Energy Storage Technologies (EST) Laboratory. This set was the second set of capacitors received from SAFT and represented their technology as of October 1997. All the capacitors were based on an experimental carbon electrode/non-aqueous electrolyte technology. The ten capacitors were rated at 0.5 to 3.0 V with capacitances varying from 135 F to 138 F. Constant-current and constant-power tests [2] were conducted on each capacitor; the test parameters were set according to the ratings of each device and from information supplied by SAFT America, Inc. The as-tested weight of the capacitors supplied by SAFT, which included the connecting wiring, varied from 0.03179 kg to 0.033317 kg. The volume of the devices was (64.95 mm height x 18.52 mm diameter) equal to 0.0175 liters. These devices were based on the #18650 container size used in SAFT's battery development program. The constant-current test was the first test to be conducted on the capacitors and consisted of three charge and discharge cycles between 3 V and 0.5 V at constant-currents of 5 A, 10 A, 20 A, 25 A and 30 A. SAFT indicated that corrosion problems could arise if the capacitors were discharged to values less than 0.5 V. For these tests, the constant-current charging current used for each test was the same as that used for the constant-current discharge. The measured discharge voltage as a function of discharge time is presented in Figure 1 for the best dev
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